The invention relates to a device and a method for feeding sheets to a sheet-processing machine, such as a printing press especially.
A device of the foregoing type has been disclosed by German Petty Patent DE 296 15 996 U1. A guide roller is described therein, which serves as a guide device for holding down sheets to be processed. The guide roller is mounted so as to be adjustable vertically, for the purpose of adapting it to the respective paper thickness. In addition, the guide roller is adjustable with regard to the spacing thereof from front lays, the selected spaced distance from the front lays being increased in order to process sheets of thick paper and Cardboard or pasteboard, respectively, because of the comparatively low flexibility of materials of this type.
The great distance of the guide roller from the front lays, which therefore in principle signifies an advantage in the processing of (board) sheets, because the (comparatively inflexible) sheets may easily be fed over the front and top lays and to the relevant feeder drum in this way, has a disadvantageous effect with regard to a first sheet, in that the first sheet cannot be guided adequately securely under the top lays as the first sheet is brought up to the front lays. It is possible for so-called overshoots to occur here.
A further disadvantage of the heretofore known guide device according to the aforementioned German Petty Patent DE 296 15 996 U1 is that the guide device is fixed to the frame on the feed table and makes accessibility to the front/top lay and to a pregripper more difficult. In addition, clearing the feed table, as is required when so-called stoppers occur, is thereby hampered.
It is accordingly an object of the invention to provide a device and a method for feeding sheets to a sheet-processing machine, especially a printing press, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which a guide device is configured in such a way that secure and marking-free sheet feeding without any xe2x80x9covershootsxe2x80x9d is assured, and indeed, especially in the case of sheets of thick paper and board as well. In addition, when the front lay guard is opened, no disruptive superstructures should make accessibility to the feed table and to the front/top lay more difficult.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for feeding sheets to a sheet-processing machine, particularly a printing machine, comprising a feeding table. Front lays are disposed at a front end of the feeding table, as viewed in a sheet-conveying direction. A first guide device is disposed immediately upstream from the front lays, as viewed in the sheet-conveying direction, and above the feeding table, and is adjustable vertically with respect to the feeding table. A second guide device is disposed upstream from the vertically adjustable first guide device, as viewed in the sheet-conveying direction. The second guide device is disposed in a position oriented parallel to the first guide device.
In accordance with another feature of the invention, the sheet-feeding device further comprises an upwardly pivotable-away front lay guard. The first guide device is disposed on the front lay guard so as to be pivotable about an axis oriented transversely with respect to the sheet-conveying direction.
In accordance with a further feature of the invention, the pivot axis of the first guide device is disposed in such a way that as a distance of the first guide device to the feeding table increases, a distance of the first guide device to the front lays simultaneously becomes greater.
In accordance with an added feature of the invention, the sheet-feeding device further comprises a pneumatic cylinder disposed on the front lay guard. The pneumatic cylinder serves for vertically adjusting the first guide device.
In accordance with an additional feature of the invention, the sheet-feeding device further comprises a separating-shoe profile pivotably disposed on the front lay guard. The first guide device has a plurality of guide rollers oriented coaxially with one another in a row and mounted on the separating-shoe profile.
In accordance with yet another feature of the invention, the second guide device, in comparison with the first guide device, has at most only a few guide rollers disposed at comparatively large axial distances from one another.
In accordance with yet a further feature of the invention, the second guide device is also disposed, at least partly, on the front lay guard.
In accordance with yet an added feature of the invention, the sheet-feeding device further comprises a pulling device for lateral sheet alignment. The second guide device is connected, at least partly, to the pulling device.
In accordance with yet an additional feature of the invention, the second guide device includes a central guide roller and two lateral guide rollers. The central guide roller is assigned to the front lay guard, and the two lateral guide rollers are respectively assigned to the pulling device.
With the objects of the invention in view, there is also provided a method of feeding sheets, which comprises providing a sheet-feeding device having a first guide device. The first guide device is positioned into an operating position close to a surface of a feeding table for processing a first sheet. The first guide device is adjusted into a stop position at a greater distance from the feeding table for processing further sheets following the first sheet.
In accordance with another mode of the invention, the method further comprises providing sheets of thick paper and board to be respectively fed, having a thickness of at least approximately 0.3 mm to at least approximately 0.6 mm.
With the objects of the invention in view, there is additionally provided a method of feeding sheets, which comprises providing a device for feeding sheets to a sheet-processing machine, including a feeding table. Front lays are disposed at a front end of the feeding table, as viewed in a sheet-conveying direction. A first guide device is disposed immediately upstream from the front lays, as viewed in the sheet-conveying direction, and above the feeding table, and are adjustable vertically with respect to the feeding table. A second guide device is disposed upstream from the vertically adjustable first guide device, as viewed in the sheet-conveying direction. The second guide device is disposed in a position oriented parallel to the first guide device. The first guide device is positioned into an operating position close to a surface of the feeding table for processing a first sheet. The first guide device is adjusted into a stop position at a greater distance from the surface of the feeding table for processing further sheets following the first sheet.
According to the invention, therefore, the first guide device (close to the front lay) in the (lowered) operating position thereof, apart from the xe2x80x9cnormal casexe2x80x9d of processing sheets of thin paper, serves and is required, respectively, for the first sheet only, when processing sheets of thick paper or board, i.e., cardboard or pasteboard, (in order to prevent xe2x80x9covershootsxe2x80x9d). For succeeding sheets of thick paper or board, on the other hand, the guide function is performed only by the second guide device according to the invention, which is disposed farther away from the front lays, while the first guide device is here located in the (raised) stop position. Accordingly, the comparatively low flexibility of sheets of thick paper or board is taken optimally into account.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device and a method for feeding sheets to a sheet-processing machine, especially a printing press, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.